Electrical coil structure



Sept. 25, 1962 w. R. BAKER ETAL 3,056,071 ELECTRICAL COIL STRUCTURE Filed Feb. 12, 1959 INVENTORS. WILLIAM R. BAKER BY ARTHUR HARTWIG ATTORNEY.

United States Patent O 3,056,071 ELECTRICAL COIL STRUCTURE William R. Baker, Oriuda, and Arthur Hartwig, Richmond, Calif., assignors to the United States of America as represented by the United States Atomic Energy Commission Filed Feb. 12, 1959, Ser. No. 792,932 3 Claims. (Cl. 317-158) The present invention relates to electrical coils, and more particularly to a novel structure for a high current electrical coil, such as the winding of a large electromagnet, wherein circulation of a substantial amount of coolant fluid through the coil is necessary to provide adequate cooling.

A common means for cooling large high current coils utilizes the forced coolant technique. In this method the coil is wound of hollow conductor and a coolant fluid is circulated through the axial passage of the conductor. Such a structure is subject to several disad vantages in addition to the obvious expense of manufacturing hollow conductors. One difliculty lies in efficiently forcing a coolant through the extremely long, constricted and curved coil passage. The frictional resistance to coolant flow in the passage creates a sizable pressure differential along the flow passage thereby necessitating an unduly large pumping pressure. If the hollow passage is constructed with a larger diameter cross section in order to reduce the pumping pressure required, the coil is resultingly less compactly wound, i.e., has fewer turns per cross-sectional area, with deleterious results from the electrical standpoint.

Another method commonly employed to cool electrical coils is to maintain the coil immersed in a coolant bath, such as the oil in a transformer case. If the coil is subjected to a high current the oil in some instances is circulated, or water coils are immersed in the oil bath as a means of removing heat. In either case, as the coil is wound compactly, thereby leaving little space between the turns, a substantial amount of coolant is not circulated through the interspaces between the turns, and therefore a relatively low limit exists as to the rate at which heat can be transferred to the coolant.

In view of the stated disadvantages of conventional coils a need exists for a coil structure which can carry an extremely high current and yet be sufficiently cooled without necessitating an unduly high pumping pressure to circulate a coolant. It is further desirable that maximum surface contact between a coolant and the coil turns exists without occasioning a substantial loss of coil compactness, and that in order to be generally useful, economical and adaptable to various applications the overall coil construction should be simple.

Coils having the foregoing advantageous characteristics are particularly needed in such applications as energizing large extremely powerful electromagnets of the type utilized in charged particle accelerators particularly where such magnets are of the pulsed variety. Magnets of this type are also widely employed in the current efforts to achieve controlled thermonuclear reactions. Other instances where intense currents must be circulated through a compactly wound coil are common and will suggest themselves to those skilled in the art.

The present invention overcomes the disadvantages of the conventional structures and provides a high current coil requiring only minimum coolant pumping pressure in a structure where heat transfer is maximized. Replacing the conventional hollow tubular conductor or the wrapped wire coil is a flat strip of conductor wound in a tight spiral. One surface of the conductor is scored With parallel transverse grooves which constitute, when the conductor is wound into spiral form, a plurality of 3,056,071 Patented Sept. 25, 1962 short longitudinal coolant passages distributed uniformly throughout the coil. To provide insulation between adjacent turns of the coil a matching fiat sheet of suitable dielectric is wound with the conductor. Coolant liquid is easily pumped through the short parallel coolant channels of the coil, and in passing therethrough effects an excellent heat transfer. The short straight channels of the coil offer relatively little resistance to coolant flow, and as a result a high rate of flow is achieved with little pressure exerted by the pump. The invention therefore not only eliminates the principal difficulties encountered in the prior structures, but is further characterized by a simplicity of construction and operation.

It is accordingly an object of the present invention to provide an improved electrical coil capable of carrying extremely high currents.

It is another object of the invention to provide a novel high current electrical coil structure which structure has provision for highly eflicient cooling.

It is an important object to provide a coil structure particularly adapted for the excitation of large electro magnets.

A further object of the invention is to provide a simple and economically manufactured high current electrical coil structure.

Still a further object of the invention is to provide a high current electrical coil which is of rugged construction and capable of withstanding the thermal and magnetic shock brought about by the sudden application of intense currents.

The invention, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the following specification taken in conjunction with the accompanying drawing, in which:

FIGURE 1 is a top view of the apparatus, with portions of the upper surface thereof broken away,

FIGURE 2 is an enlarged view of the encircled portion of FIGURE 1 illustrating the detailed structure of the winding in the coil,

FIGURE 3 is a perspective view of a section of the conductor of which the coil is wound, and

FIGURE 4 is a section view taken along line 44 of FIGURE 1 and further clarifying the general construction of the coil.

Referring now to the drawing and more particularly to FIGURE 1 thereof, there is shown in phantom cross section a simple cylindrical electromagnet core 11, which in the present embodiment constitutes the element about which a coil is disposed. It should be emphasized that the core 11 may be any desired configuration about which coils are normally wound, for example, C-shaped magnets, U or H-shaped magnets and the like, which magnets are configurated for various purposes understood in the art. The coil 10 may also be an integral component of a transformer, inductor or other apparatus which utilizes high current coils, and is particularly suitable, as exemplified by the present embodiment, for exciting large high current electromagnets. It should further be understood that the core 11 is not an element of the invention but is shown merely to illustrate one application thereof, the invention being usable in the construction of air-core coils.

The coil 10 comprises a long flat rectangular strip 12 of electrical conductor such as copper, copper being ductile as well as a good conductor, although other conductors more rigid than copper may be wound in this fashion when heated. Disposed against one face of the conductor 12 is a matching flat rectangular strip 14 composed of a dielectric material which material is also preferably ductile or flexible. The two strips 12 and 14 are tightly wound in a spiral thereby forming the annular coil structure 10, which structure is thus characterized by tightly wound alternate turns of conductor and dielectric, as best shown in the enlarged FIGURE 2.

Referring now to FIGURE 3, which shows a perspective view of a small section of the conductor 12, one face of the conductor is scored by parallel grooves 13, the grooves being aligned transverse to the long dimension of the conductor. Without departing from the general principles of the invention or the advantageous properties thereof, the grooves 13 may also be disposed parallel with the long dimension of the conductor 12, slant diagonally across the conductor surface, or be arranged in any other suitable pattern across the conductor surface. The grooves 13 need not necessarily be straight or parallel, although such form results in minimum length of the grooves and therefore minimizes the resistance to coolant flow.

The grooves 13 are preferably shallow and have relatively short sidewalls 15 and a wide base surface 20. Such shallow grooves 13 minimize differences in resistance to electrical current offered by different portions of the conductor 12 along the total conductor surface and maximize the effective heat transfer between the conductor and coolant circulating through the grooves.

The grooves 13 collectively form a plurality of short parallel coolant passages, distributed uniformly throughout the coil structure when the conductor 12 is wound into spiral form. Obviously the more shallow the grooves 13 the more compactly the conductor 12 and dielectric 14 can be wound. Very shallow grooves can be made wider in order to maintain a selected cross-sectional groove area and thereby avoid unduly constricted coolant fluid flow through the passages. It should be observed that, as the grooves 13 are formed in the conductor 12, a coolant fluid flowing through the groove passages has direct contact with the heat generating conductor surface throughout the passages through the coil, and therefore heat is directly and efficiently transferred to the coolant fiuid. It will be apparent, however, that the grooves can be made in the dielectric 14, if desired, rather than in the conductor 12.

As shown in FIGURES l and 4, the coil 10 is disposed inside an annular casing or housing 16, the central bore thereof being occupied by the electromagnet core 11; the casing comprising an outer sidewall 17, an inner sidewall 18, a fiat annular bottom plate 19, and a matching top plate 21. Such casing 16 serves to provide a fluid tight enclosure for the coil structure 10 in order to facilitate the circulation of the coolant through the coil.

Transpiercing the lower portion of the outer sidewall 17 is a coolant inlet conduit 22, and extending from the top plate 21 is an outlet conduit 23, the conduits being connectable to a source of liquid coolant under pressure. A filter element 40 is disposed inside the inlet conduit 22 near the casing 16 in order to strain the coolant and thereby assure smooth flow thereof through the grooves 13. While the invention has been described as utilizing a liquid coolant, it will be understood that in some adaptations of the invention a gaseous coolant such as air may be preferable.

Although in the present embodiment the coil 10 and enclosing casing 16 are disposed with the axis thereof upright, it should be observed that other orientations are possible without loss of operating elliciency; for example, the structure can just as readily be disposed on its side.

To provide means for dispersing the coolant flow to all of the grooves 13 there are disposed between the top plate 21 and the top of the wound coil 10 a plurality of annular, concentric, spaced apart ribs 24 composed of dielectric material which ribs are secured to the top of insulative radial crosspieces 30 that extend between the inner side wall 18 and the outer sidewall 17 of the casing 16. Similarly disposed between the bottom plate 19 and the bottom of the wound coil 10 is another set of spaced annular ribs 26, which are secured to the bottom surfaces of a second set of radial crosspieces 27. The insuiative crosspieces 27 and 30 contact relatively small areas of the bottom and top ends of the wound coil 10 and accordingly coolant flow blockage at the ends of the grooves 13 is negligible. The coolant fluid, in this instance transformer oil, enters the casing 16 through the inlet conduit 22, flows through the channels 25 between the bottom ribs 26, up through the grooves 13, through the channels 25 between the top ribs 24, and exits through the outlet conduit 23. In operation, all of the interspaces inside the casing 16 are filled with the rapidly flowing transformer oil. The ribbed structures efficiently provide insulative support for the wound coil 10 and appropriate spacing of the coil apart from the casing top and bottom plates 21 and 19. To facilitate coolant distribution various other suitable spacer and support mechanisms might be employed consistent with design requirements of a particular embodiment of the invention.

To insulate the conductor 12 from the inner sidewall 18 and from the outer sidewall 17 of the casing 16 an annular insulation band 28 is disposed between the inner sidewall and the conductor, and another larger insulation band 29 is disposed between the conductor and the outer sidewall, glass fiber bands being a suitable material.

As shown in FIGURE 4, current is supplied to the conductor 12 through two electrical leads 31, which enter the casing top plate 21 through insulative bushings 32, each lead terminating in a thin copper strip 33, one strip being connected to the innermost turn of the coil 10, the other strip connected to the outermost turn. Because of the elliciency of the described cooling means as built into the coil structure, the electrical current carried by the conductor 12 can be extremely high. Heat generated by electrical resistance is transferred from the conductor 12 directly to the flowing coolant which coolant is circulated out of the coil. As the grooves 13 from which heat is removed are an integral part of the conductor 12, the conductor is maintained at a temperature well below that which would cause softening or melting of the conductor or charring of the adjacent dielectric material 14.

In operation, excitation current is supplied to the conductor 12 through leads 31 resulting in the production of heat. The coolant oil entering the casing 16 through the inlet conduit 22 fills the channels 25 between the bottom annular ribs 26 and is forced upward therefrom through the parallel straight grooves 13 of the conductor 12 and through the upper ribs channels 25' into the outlet conduit 23. In passing through the grooves 13 the coolant oil absorbs the internally generated heat from the conductor 12.

A substantial amount of coolant can be pumped through the groves 13 at a high flow rate, and in being pumped therethrough creates a relatively small pressure differential, for the numerous straight grooves 13 offer minimum resistance to the coolant flow.

In general, the coil structure herein described may replace any coil cooled by the forced coolant method. Numerous modifications of the simple, basic structure, i.e., alternate layers of grooved, fiat conductor and flat dielectric spirally wound to form a coil having longitudinal coolant passages, are possible and will readily suggest themselves to those skilled in the art.

Thus while the invention has been disclosed with respect to a single embodiment, it will be apparent to those skilled in the art that numerous variations and modifications may be made within the spirit and scope of the invention and thus it is not intended to limit the invention except as defined in the following claims:

What is claimed is: p

1., An electrical coil for use in high current circuits comprising, in combination, a long flat strip of electrical conductor formed in an open-centered spiral configuration, at least one surface of said conductor having a plurality of generally transversely aligned shallow grooves said grooves being recessed in said conductor surface and being separated by relatively broad flat areas of said surface, terminal means at each end of said conductor for applying electrical current thereto, and a quantity of electrically insulative material formed in a spiral configuration similiar to that of said strip of conductor material and interlaminated therewith to form a unitary annular coil structure characterized by alternated turns of conductor and insulator and further characterized by transverse coolant passages formed by said grooves.

2. An electrical coil substantially as described in claim 1 and in which said transverse grooves are equally distributed along substantially the entire length of said surface of said conductor.

3. An electrical coil structure substantially as described in claim 1 and wherein said shallow grooves are linear and evenly spaced along said surface of said conductor 15 and are aligned substantially at right angles to the long dimension thereof.

References Cited in the file of this patent UNITED STATES PATENTS Conte July 15, Neall Oct. 11, Long June 6, Paluev Nov. 6, Bilodeau Mar. 17, Gaston June 14, Gray et al. Dec. 2, Diebold April 14,

FOREIGN PATENTS Germany June 4, 

